Vacuum reactor for vapor deposition on continuous filaments



July 1, 1969 Filed July 21, 1967 R. B. REEVES ETAL VACUUM REACTOR FOR VAPOR DEPOSITION ON CONTINUOUS FILAMENTS Sheet WI /2 II'IIIPIIIV INVENTORS. JoH/v QCoL/LTER,

AGENT July 1, 1969 R. B- REEVES ETAL VACUUM REACTOR FOR VAPOR DEPOSITION ON CONTINUOUS FILAMENTS Filed July 21, 1967 Sheet 2 012 /N VENTORS.

JOHN Q. Co ULTER,

R. ER uc REEVES AGENT United States Patent O 3,452,711 VACUUM REACTOR FOR VAPOR DEPOSITION ON CONTINUOUS FILAMENTS Robert Bruce Reeves, Phoenixville, and John Q. Coulter,

Philadelphia, Pa., assignors to General Electric Company, a corporation of New York Continuation-impart of application Ser. No. 588,936, Oct. 24, 1966. This application July 21, 1967, Ser. No. 669,995

Int. 'Cl. C23c 13/12 US. Cl. 11849.5 7 Claims ABSTRACT OF THE DISCLOSURE INTRODUCTION This application is a continuation-in-part of copending application Ser. No. 588,936, Reeves and Coulter, filed Oct. 24, 1966', now abandoned, and assigned to the assignee of the present invention. The invention disclosed herein relates to apparatus for conducting a coating operation at reduced pressure on a moving substrate of indefinite length and more particularly to a vacuum reactor for depositing a high quality coating onto a filament of indefinite length by a high temperature gas decomposition process.

BACKGROUND OF THE INVENTION Coating processes involving the decomposition of a gaseous compound are well known. The use of such processes to deposit a coating onto a filamentary substrate of indefinite length has recently been the subject of much investigation. If a very fine filamentary substrate is used and the coating is almost completely free of imperfections and crystallinity, a high strength filament, comprised primarily of a decomposition product of the gaseous compound results. Such filaments are highly promising as the reinforcing constituent of ultrahigh strength composite materials. Two problems which have been encountered in producing filaments of this type are that, first, coatings of this kind often cannot be produced unless the deposition process is carried out in an atmosphere almost completely devoid of any contaminants. Second, density and strength considerations impose the requirement that the core material or filamentary substrate be as fine and as light as possible. The filamentary substrates used therefore are extremely delicate. For these reasons, apparatus intended for continuously producing a strong filament of indefinite length by deposition onto a suitable core material must be capable of maintaining a high vacuum and low concentration of contaminants in the coating space of the apparatus and further must exert a minimum of mechanical force, such as frictional drag, on the core material or filamentary substrate as it passes through the apparatus. No such apparatus has heretofore been available.

With a view to these and other problems, it is an object of the present invention to provide a suitable apparatus 3,452,71 l Patented July 1 1969 ICC for producing a high quality coating on a thin filamentary substrate of indefinite length.

Another object of this invention is to provide a means for maintaining a high vacuum and a low concentration of contaminants in a space as a coating material is continuously deposited onto a very fine filamentary substrate of indefinite length.

Still another object of this invention is to provide coating apparatus with a coating chamber in which a high vacuum and a low concentration of contaminants can be maintained while a filamentary substrate of indefinite length is continuously passed through the chamber.

It is also an object of the present invention to provide apparatus for coating a continuously moving, very fine filamentary substrate of indefinite length in which a minimum of mechanical force is exerted on the filamentary substrate by the apparatus.

A further object of this invention is to provide coating apparatus for a continuously moving filamentary substrate in which repeated electrical contact is made with said substrate in such apparatus, having a convenient means for assembling and preparing said apparatus for operation.

BRIEF SUMMARY OF THE INVENTION These and other objects are met, in accordance with the present invention, by a coating apparatus comprising a coating chamber including an evacuating means and an inlet for coating gas, and further including entrance and exit passageways, at opposite ends of the chamber, slightly larger than the filamentary substrate for which the apparatus is intended. This apparatus also includes, in communication with the entrance passageway, a vacuum seal chamber which in turn communicates through an additional filament passageway with an inert gas purge chamber. The inert gas purge chamber also includes an additional filament passageway through which a filament to be coated is introduced to the apparatus.

In the preferred form of the present invention, the apparatus also includes a second vacuum seal chamber and a second inert gas purge chamber which communicates successively with the exit passageway of the coating chamber. In addition, the coating chamber includes electrical contacts for making low friction electrical connection with conductive filamentary substrates so that these substrates may be heated in this way, within the coating chamber, to a temperature at which decomposition of a coating materials is is effected. The preferred form of the apparatus of the present invention also includes a gas collimator, which is a gas flow director or battle with a slotted passageway generally corresponding in length to the length of the filamentary substrate in the coating chamber, disposed between the filament and the coating gas inlet. Further, the coating chamber is a vertically disposed tubular space divided into stages of predetermined length to maximize deposition rate throughout the reactor. These stage dividers comprise mercury reservoirs, each with an opening in the bottom thereof for permitting passage of the filamentary substrate and the material coated thereon through the reservoirs without permitting leakage of mercury, said reservoirs being in electrical contact with the filament and being attached to sources of electrical potential to maintain a resistive heating circuit at each stage of the reactor. All of the mercury electrical contacts in the preferred form of this invention are main tained in fixed position with respect to one another so that they may be moved in toto from the coating chamber.

DETAILED DESCRIPTION OF THE INVENTION While the Specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the present invention, this invention may be 3 better understood from the following description, taken in conjunction with the following drawings, in which:

FIGURE 1 is a side View of one form of the present invention;

FIGURE 2 is a cross section of the main reaction space of the apparatus illustrated in FIGURE 1;

FIGURE 3 is a horizontal cross section of one end of the reaction chamber of the apparatus illustrated in FIGURE 1;

FIGURE 4 is another horizontal cross section of one end of the reaction chamber of the apparatus illustrated in FIGURE 1;

FIGURE 5 is a cross sectional view of the top of the preferred form of the present invention; and

FIGURE 6 is horizontal cross section of the coating chamber shown in FIGURE 5.

Referring more specifically to FIGURE 1, there is shown a generally tubular coating apparatus comprising a main reaction or coating chamber 1, outer chamber housings 2 on either end of the main reaction chamber 1, coating material, generally gas, inlets 3, main vacuum lines 4, auxialiary vacuum lines 5, inert gas purge inlets 6, inert gas purge outlets 7, and a series of pairs of electrical leads 8 entering the main reaction chamber 1.

A vertical cross section, in the plane 2-2, through the main reaction chamber of the apparatus illustrated in FIGURE 1, may be seen in FIGURE 2. In particular in FIGURE 2, there is shown the main reaction chamber 1, an auxiliary vacuum line 5, an inert gas purge inlet 6, an inert gas purge outlet 7, and the coating gas flow director 11 having an opening 12 therein.

Also shown in FIGURE 2 is an electrical lead 8, which enters the main reaction chamber 1 and contacts a mercury standpipe 9 having slots therethrough near the centerline of the tubular reaction chamber 1. The mercury standpipe is a tubular receptacle for mercury, about V inch in diameter. It includes vertical slots 10, about & inch wide. When this tube is filled with mercury, a low friction electrical contact may be made through the mercury to a conductive filament passing through the slots 10. The surface tension of mercury is sufficiently high to prevent seepage of mercury through these slots or slotted passages. The electrical contacts, made by these mercury standpipes, are used to heat resistively a conductive filamentary substrate as it passes through the apparatus and thereby to effect thermal decomposition of a coating material, generally a gaseous coating material.

A better view of the coating gas flow director 11, with slotted opening -12, may be seen in FIGURE 3, which is a horizontal cross section in the plane 33 of the cross section shown in FIGURE 2. Also in FIGURE 3 there is seen the electrical lead and mercury standpipe 8 and 9, and a portion of the main reaction chamber 1. Main reaction chamber 1 is sealed from the outer housing chamber 2 by means of an 'O-ring 13. Other elements shown in FIGURE 3 are auxiliary vacuum line 5 an inert gas purge inlet 6, an inert gas purge outlet 7, the outer end 14a and the inner end 14b of an outer chamber housing 2, and an outer chamber tube 15.

In FIGURE 4 there is shown another horizontal cross section, this one in the plane 44 of the cross section shown in FIGURE 2. In FIGURE 4 there is again shown the main reaction chamber 1, an electrical lead 8, a mercury standpipe 9, slots 10 therein, an outer chamber housing 2, with its ends 14a and 14b, the O-ring seal 13 between the outer chamber housing and the main reaction chamber, an auxiliary vacuum line 5, an inert gas purge inlet 6, an inert purge outlet 7, and an outer chamber tube 15. In addition, there is seen a first outer chamber 16, separated from a second outer chamber 17 by an outer chamber divider 18. Very small passageways .19, 20, and 21 are provided, respectively in the outer end 14a of the outer chamber housing 2, the outer chamber divider 18, and the inner end 1412 of the outer chamber housing 2. The size of these passageways, which are preferably small to limit gas flow between chambers, is dependent on the nonimal diameter and the regularity in diameter of the substrate being coated. Generally, the passageways are slightly larger than the substrate or, stated conversely, as small as possible without interfering with the passage of the substrate through the passageways. For example, if a carbon-coated silica filament 0.7 mil in nominal diameter is the substrate, the passageways 19, 20, and 21, may be about 8 or 9 mils in diameter without either interfering with the moving substrate or permitting an objectionable amount of gas flow between chambers.

The apparatus illustrated in FIGURES 1-4 may be made from any non-reactive material which can withstant the pressures and temperatures of the coating process. Although glass has been used in the laboratory forms of this invention, metal or plastic would probably be preferred for an apparatus of any substantial size.

With regard now to one mode of opeartion of this apparatus, a filamentary substrate to be coated is passed lengthwise through the tubular reaction chamber from passageway 19, at the left of FIGURE 1, to passageway 19, at the right of FIGURE 1. As the filament passes into the first outer chamber 16, through passageway 19, inert gas is passed through the first outer chamber which acts as an inert gas purge chamber to remove any air which may leak through the filament passageway 19. The inert gas purge operates at a pressure slightly above atmospheric.

From the first outer chamber 16, the substrate passes to the second outer chamber 17 through passageway 20.

In the second outer chamber 17, a vacuum through the auxiliary vacuum line 5 which further acts to hold down the pressure in the main reaction chamber 1 and also to minimize the concentration of contaminants therem.

As the filament passes through the passageway 21 in the inner end 1412 of the outer chamber housing 2, it enters the main reaction space of the apparatus, the interior of the main reaction chamber 1, which is evacuated through main vacuum lines 4. The cumulative effect of the primary vacuum system, i.e. main vacuum lines 4, the secondary vacuum system, i.e. auxiliary vacuum lines 5, the inert gas purge chambers, and the small passageways limiting gas flow between chambers, is that an extremely high vacuum and an extremely low concentration of contaminants may be maintained in the interior of the main reaction chamber 1. Further this is done without sacrificing the capability of the apparatus to handle very fine, and therefore very Weak filamentary substrates.

In the apparatus shown, heating of conductive substrates is accomplished by means of resistance heating within the coating chamber. For this purpose, electrical leads, which contact the filament as it progresses through the tubular reaction chamber, are provided. These electrical contacts comprise, in the apparatus shown in FIG- URE 1, the elements designated as the electrical leads 8, and the mercury standpipes 9 having slots 10 through which the filament passes. Although suflicient current may be established in the conductive filament or conductive-coated filament by means of a pair of electrical leads, more efiicient heating may be produced in a long tubular reactor of the type illustrated by use of a plurality of pairs of electrical leads as shown in FIGURE 1.

The coated filamentary substrate leaves the coating chamber and the apparatus by passing successively through passageway 21, second outer chamber 17, passageway 20, first outer chamber 16 and passageway 19, all at the right of FIGURE 1. Conditions in the outer chambers at the right of FIGURE 1 are the same as, and these elements perform the same function as, those at the left of FIGURE 1 through which the substrate enters the main reaction or coating chamber.

Referring now to FIGURE 5, there is shown the top section only of another form of apparatus within the scope of the present invention. In this, the preferred form of the present invention, a removable inner assembly is provided in the coating chamber for resistively heating conductive filament passing through the coating chamber. This assembly includes a plurality of sections or stages whereby segments of filament in the chamber are heated independently so that a given section of filament passing through the chamber is repeatedly heated during its passage through the chamber. Specifically, this form of the invention comprises a vertically disposed tubular coating chamber 22 with dual entry chambers 23, which include filament passageways 24, inert gas purge inlets 25 and outlets 26, and vacuum lines 27. Coating chamber 22 is secured to dual entry chambers 23 by threaded sleeves 28 and sealed by O-rings 29. Coating chamber 22 also includes coating gas inlet line 30 and vacuum line 31. The interior of coating chamber 22 is divided into stages by stage separators 32. One such stage is shown in FIGURE 5. Stage separators 32 are fastened to one another with selected distances therebetween, by electrically non-conductive rods 33 and coating gas deflector 34 which defines a slotted opening between coating gas inlet line 30 and the centerline of chamber 22. Mercury cups 35 disposed along the centerline of chamber 22, include a jeweled bearing 36 having a vertical opening therethrough only slightly larger than the diameter of the filament to be processed in the reactor. Cups 35 and separators 32 are formed of an electrically conductive material, such as brass, through which electrical contact is made between mercury in cups 35 and electrical contacts 37 on the inner wall of coating chamber 22. When an electrically conductive filament passing through the various filament passageways and mercury cups is to be heated, an electrical potential is established by electrical leads 38, which enter coating chamber 22 and contact electrical contacts 37.

Some of the details of the coating chamber and stage separators shown in FIGURE 5 may be better seen in FIGURE 6 which is a horizontal cross section of the coating chamber shown in FIGURE 6. Also seen in FIG- URE 6 is an indentation 39 in stage separator 32 which permits vertical insertion of the assembled stage separat6rs, connecting rods, bafiies, and mercury cups, with a filamentary substrate threaded therethrough, by dropping this assembly into the vertically disposed coating chamber with indentation 39 in registry with electrical contacts 37 on the inner walls of coating chamber 22. When the assembly is fully inserted, it is rotated about 80 degrees counter-clockwise into the final position shown in FIG- URES 5 and 6.

The convenience in preparing to operate and in operating the apparatus shown in FIGURES 5 and 6 is apparent. Threading of a very fine filamentary substrate through all of the mercury contact cups in the stage separators is greatly facilitated by having stage separators removed as an assembly from the coating chamber. It is this feature in particular which renders this particular form of the invention highly feasible.

Other modifications which can be made in the apparatus of the present invention include the optimization of the distances between stage separators. This may vary through the reactor depending upon the localized rate of deposition. For example, in the vacuum decomposition of diborane onto a resistively heated carbon coated silica substrate, deposition occurs for only a short length beyond the resistive heating contact of the first stage. Therefore, the first stage as shown in FIGURE 5 may be short. Successive stages may be progressively longer. In a particular form of the apparatus shown in FIGURE 5, stage lengths of 2, 4, 4, 6, 6, and 6 inches, respectively are used.

Following are several examples of processes in which the apparatus of the present invention has been used.

A reactor of the type shown in FIGURES 1-4 with a main reaction chamber about 28 inches long has been used to produce a high quality, very pure amorphous boron coating on a carbon-coated silica substrate filament having a nominal diameter of about 0.7 mil. The product was a 4 mil boron filament which had very high tensile strength and modulus of elasticity. The silica filamentary substrate was passed through the reactor at a rate of about 7 feet per minute while the coating chamber was held at about 2 millimeters mercury absolute. The filamentary substrate was repeatedly heated to 700 degrees centigrade by several pairs of electrical leads dividing the coating chamber into several stages of equal length. Diborane gas was fed at a rate of about cubic centimeters per minute (measured at standard conditions of temperature and pressure) at 6 points in the main reaction chamber and a 35 mil slot width was used in the gaseous flow director or gas collimator in the main reaction chamber. A deposition rate of aproximately 650 mils per hour was attained. With similar process conditions, 4 mil boron filament has been made in the apparatus illustrated in FIGURES 5-6 at a rate approaching 20 feet per minute.

In another experiment in which the apparatus of the type shown in FIGURES 1-4 was used, a 2 mil tungsten filamentary substrate was drawn through the reactor at about 18 feet per minute. Diborane was passed across the filament at about 20 cubic centimeters per minute per inch of filament in the coating chamber. The filamentary substrate was heated to about 750 degrees centigrade and the reactor pressure was held at about 20 millimeters of mercury absolute. A very smooth 4 mil borontungsten filament was obtained in this experiment.

In another similar process, a mixture of 30 cubic centimeters per minute of acetylene, cubic centimeters per minute of diborane and 20 cubic centimeters per minute of hydrogen was passed through the coating chamber of the apparatus of the present invention. A tungsten filament substrate heated to about 860 degrees centigrade was passed through the apparatus. A coating chamber pressure of about 5 millimeters mercury absolute was maintained. These materials and conditions resulted in the production or a .good quality boron carbide deposit on the tungsten substrate.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for conducting a continuous vacuum coating operation on a moving filamentary substrate of indefinite length including:

(a) an inert gas purge chamber,

(b) a vacuum sealed chamber adjacent said inert gas purge chamber,

(cl)a a coating chamber adjacent said vacuum seal cham- (d) means for passing an inert gas through said inert gas purge chamber,

(e) means for evacuating said vacuum seal chamber,

(f)3 a separate means for evacuating said coating cham- (g) means for admitting a coating material into said coating chamber,

(h) means for allowing the passage of said substrate through said inert gas purge chamber, said vacuum seal chamber and said coating chamber, said means comprising openings slightly larger than the filamentary substrate,

(i) a second vacuum seal chamber said coating chamber,

(j) a second inert gas purge chamber adjacent said second vacuum seal chamber,

(k) means for evacuating said second vacuum seal chamber,

(1) means for passing inert gas through said second inert gas purge chamber,

(in) means for successively passing said substrate from said coating chamber through said second vacuum located adjacent to seal chamber and said second inert gas purge chamber, said means comprising openings slightly larger than the filamentary substrate, and

(11) means for directing said coating material into the space immediately surrounding said moving substrate, said coating directing means comprising a bafile disposed between said coating material admitting means and said substrate, said baflle having a slotted opening extending along said substrate.

2. Apparatus, such as that recited in claim 1, wherein each of said chambers is generally linearly disposed from all of the remaining said chambers.

3. Apparatus, such as that recited in claim 1, including means for heating said substrate during its travel through said coating chamber.

4. Apparatus, such as that recited in claim 3, wherein said substrate is electrically conductive and said heating means comprises an electrically resistive heating circuit contacting said substrate by mercury reservoirs in the coating chamber through which said substrate passes.

5. Apparatus, such as that recited in claim 4, wherein said coating chamber includes a removable inner assembly comprising a series of mercury cups spaced at preselected distances from one another and in vertical alignment with one another, each having an opening sufficiently large 25 to pass a filament vertically therethrough without loss of mercury contained in said cup, and means for establishing an electrical potential between any two of said cups whereby conductive filaments disposed between said cups may be resistively heated.

6. Apparatus, such as that recited in claim 5, wherein said removable assembly includes the means for directing said coating material into the space immediately surrounding said moving substrate.

7. Apparatus as in claim 6 wherein the slot opening is substantially coextensive with said substrate.

References Cited UNITED STATES PATENTS 1,144,595 6/1915 Henderson 118-48 X 2,656,283 10/1953 Fink et al 118--48 X 2,877,138 3/1959 Vodonik 1l7-93 2,898,230 8/1959 Bullott 11849.5 X 2,801,607 8/1957 Vodar et al. 118-49.1 2,939,943 6/ 1960 Walter 118-49.5 X 3,130,073 4/1964 Van Der Linden et al. 1l793 X 3,313,269 4/1967 Hough 11849.5

FOREIGN PATENTS 766,459 1/ 1957 Great Britain.

MORRIS KAPLAN, Primary Examiner. 

